Structure-activity relationship of dihydropyridines for rhabdomyosarcoma.

Childhood muscle-related cancer rhabdomyosarcoma is a rare disease with a 50-year unmet clinical need for the patients presented with advanced disease. The rarity of ∼350 cases per year in North America generally diminishes the viability of large-scale, pharmaceutical industry driven drug development efforts for rhabdomyosarcoma. In this study, we performed a large-scale screen of 640,000 compounds to identify the dihydropyridine (DHP) class of anti-hypertensives as a priority compound hit. A structure-activity relationship was uncovered with increasing cell growth inhibition as side chain length increases at the ortho and para positions of the parent DHP molecule. Growth inhibition was consistent across n = 21 rhabdomyosarcoma cell line models. Anti-tumor activity in vitro was paralleled by studies in vivo. The unexpected finding was that the action of DHPs appears to be other than on the DHP receptor (i.e., L-type voltage-gated calcium channel). These findings provide the basis of a medicinal chemistry program to develop dihydropyridine derivatives that retain anti-rhabdomyosarcoma activity without anti-hypertensive effects.

Cytogenetic and genetic pathways in therapy-related acute myeloid leukemia.

Therapy-related myelodysplastic syndrome and acute myeloid leukemia (t-MDS/t-AML) are late complications of cytotoxic therapy used in the treatment of malignant diseases. The most common subtype of t-AML ( approximately 75% of cases) develops after exposure to alkylating agents, and is characterized by loss or deletion of chromosome 5 and/or 7 [-5/del(5q), -7/del(7q)], and a poor outcome (median survival 8 months). In the University of Chicago's series of 386 patients with t-MDS/t-AML, 79 (20%) patients had abnormalities of chromosome 5, 95 (25%) patients had abnormalities of chromosome 7, and 85 (22%) patients had abnormalities of both chromosomes 5 and 7. t-MDS/t-AML with a -5/del(5q) is associated with a complex karyotype, characterized by trisomy 8, as well as loss of 12p, 13q, 16q22, 17p (TP53 locus), chromosome 18, and 20q. In addition, this subtype of t-AML is characterized by a unique expression profile (higher expression of genes) involved in cell cycle control (CCNA2, CCNE2, CDC2), checkpoints (BUB1), or growth (MYC), loss of expression of IRF8, and overexpression of FHL2. Haploinsufficiency of the RPS14, EGR1, APC, NPM1, and CTNNA1 genes on 5q has been implicated in the pathogenesis of MDS/AML. In previous studies, we determined that Egr1 acts by haploinsufficiency and cooperates with mutations induced by alkylating agents to induce myeloid leukemias in the mouse. To identify mutations that cooperate with Egr1 haploinsufficiency, we used retroviral insertional mutagenesis. To date, we have identified two common integration sites involving genes encoding transcription factors that play a critical role in hematopoiesis (Evi1 and Gfi1b loci). Of note is that the EVI1 transcription factor gene is deregulated in human AMLs, particularly those with -7, and abnormalities of 3q. Identifying the genetic pathways leading to t-AML will provide new insights into the underlying biology of this disease, and may facilitate the identification of new therapeutic targets.

Haploinsufficiency of EGR1, a candidate gene in the del(5q), leads to the development of myeloid disorders.

Loss of a whole chromosome 5 or a deletion of the long arm, del(5q), is a recurring abnormality in myelodysplastic syndromes (MDSs) and acute myeloid leukemia (AML). To identify a leukemia-related gene on chromosome 5, we previously delineated a 970-kb segment of 5q31 that is deleted in all patients examined, and prepared a transcript map of this region. EGR1 is a candidate tumor suppressor gene within the commonly deleted segment of 5q, and encodes a zinc finger transcription factor. To test the hypothesis that loss of function of Egr1 is an initiating event in the pathogenesis of AML/MDS, Egr1-deficient mice were treated with a potent DNA alkylating agent, N-ethyl-nitrosourea (ENU), to induce secondary cooperating mutations. Egr1(+/-) and Egr1(-/-) mice treated with ENU developed immature T-cell lymphomas (CD4(+), CD8(+)) or a myeloproliferative disorder (MPD) at increased rates and with shorter latencies than that of wild-type littermates. The MPD was characterized by an elevated white blood cell count, anemia, and thrombocytopenia with ineffective erythropoiesis. Biallelic mutations of Egr1 were not observed in MPDs in Egr1(+/-) mice. Our data suggest that haploinsufficiency for Egr1 plays a role in murine leukemogenesis, and in the development of AML/MDS characterized by abnormalities of chromosome 5.